There are known timepieces comprising a case inside which an electromechanical timepiece movement is arranged. Such a movement is clocked by a quartz oscillator system. For the display of time indications, such as the hour and second, hands are mounted on motors to be driven in rotation. The motors used are Lavet type motors, also called stepping motors. In these motors, a magnetically charged rotor of cylindrical shape creates a radial magnetic field in the air gap of a magnetic circuit, on which is wound a coil whose terminals are connected to a control circuit, generally an integrated circuit, supplying current pulses, each pulse causing the rotor to advance one step. The coil is formed by a very fine wire, wound on a hollow, insulating tube containing therein one part of the magnetic circuit.
These motors, located inside the watch, are subjected to shocks which may be caused by the watch being dropped or by violent movements of the user. These shocks are then likely to disrupt the operation of the motors. These disruptions consist of an uncontrolled movement of the rotor or rotors whereby their inertia causes the skipping of at least one step.
Consequently, the time indications provided by the hands are likely to no longer be accurate.
To overcome this, there exist shock detector systems. An electronic device is therefore responsible for measuring the tension induced by the motor during a shock. Indeed, an induced voltage is generated under the effect of the inertia of the rotor. This induced voltage is detected by a detector circuit which compares the induced voltage to a predetermined threshold. If the voltage is higher than said threshold, the detector circuit deduces that a shock has occurred and transmits the information to a control unit.
In response to the shock, the control unit sends the motor a blocking pulse used to block any rotation of the rotor caused by the shock.
However, a regulated voltage inverter is used to measure the induced voltage. To increase sensitivity, the motor coil is short-circuited for a short instant thereby increasing the voltage at the motor coil terminals as a result of the self-induction effect of the motor delta(U)=L*(di/dt) and the current automatically increases. This increase may cause damage to appear.